As known in the art, a fuel cell is a system for producing electric power through a chemical reaction between oxygen and hydrogen. In some fuel cell systems, the hydrogen can be provided as a liquid or gaseous hydrocarbon material such as methanol, ethanol, or natural gas.
Recently, a polymer electrolyte membrane fuel cell (hereinafter, referred to as PEMFC) has been developed in the field of fuel cells. Since the PEMFC has excellent output characteristics, a low operating temperature, and fast starting and response capabilities, it has a wide range of applications such as a mobile power source for vehicles, a distributed power source for the home or buildings, and a small-sized power source for use in electronic devices.
The PEMFC system typically includes a stack, a reformer, a fuel tank, and a fuel pump. The stack is an electricity generating assembly consisting of a plurality of unit cells. The fuel pump supplies fuel from the fuel tank to the reformer. The reformer reforms the fuel to create hydrogen gas, and supplies the hydrogen gas to the stack. Accordingly, in a PEMFC system, the fuel in the fuel tank is transferred by the fuel pump to the reformer where the fuel is reformed to generate hydrogen gas. Then, the hydrogen gas is supplied to the stack along with air supplied by a separate pump or compressor. Subsequently, the hydrogen gas and oxygen in the air are electro-chemically reacted in the stack to generate electric energy.
A portion of the power produced by the stack is consumed to drive the entire system. This portion of power consumed in driving the system is referred to as “parasitic power.”
Since a conventional fuel cell system includes a separate fuel pump for supplying fuel to the reformer, the entire system capability and its energy efficiency decreases as the parasitic power for driving the separate fuel pump increases. In addition, since a conventional fuel cell system must be provided with a space for the separate fuel pump, it is difficult to design such a system to be of a compact size.